1. Field of the DISCLOSURE
The present invention relates to an aqueous polyorganosiloxane emulsion, in particular for the coating of substrates made of textiles or the like, such as for example woven or non-woven supports, intended to produce an elastomer as a thin film, as well as to a corresponding coating process and to the products thus coated.
2. Description of the Prior Art
In many applications, the aim is to protect the textile from heat, from fire or from other assaults by a silicone elastomer layer and/or to confer on it specific properties in certain applications (dielectric properties, for example). Mention may in particular be made, as applications, of the inflatable bags used for protecting the occupants of a vehicle, known as air bags, glass braids (sheaths made of glass fabric for thermal and dielectric protection for electrical wire), conveyor belts, fire-resistant or thermally-insulating fabrics, expansion joints (flexible sleeves for rendering pipework leakproof), tents, clothes, and the like.
In particular as regards inflatable bag, of air bag type, essential properties sought for are fire and temperature resistance, impermeability to gases, behaviour with respect to ageing, and good adhesion to the textile. See in particular French Patent FR-A-2,668,106.
Silicone linings are thus produced by coating the substrate and then curing (crosslinking) the composition in order to form the elastomer.
In certain applications, for reasons of economic competitiveness, attempts are being made to apply very fine silicone layers, which becomes difficult with a 100% silicone elastomer; for example, the minimum amount which can be deposited by conventional doctor-type techniques on a 235 or 470 dtex polyamide 6,6 fabric is of the order of 40 g/m.sup.2, i.e. an average thickness of the order of 40 microns. To obtain smaller amounts, it. is necessary to resort to a silicone elastomer used in a solvent phase, which is not satisfactory from an industrial viewpoint, in particular because of environmental problems. Provision has also been made, for textile applications, for aqueous silicone oil emulsions which are noncrosslinking and without filler, which do not confer any thermo-resistance.
Neither do recent developments in filler-containing, aqueous silicone emulsions enable very low coating thicknesses to be obtained.
Thus, European Patent Application EP-A-0,535,649 provides a composition for lining inflatable bags of air bag type comprising an organopolysiloxane (A) in emulsion in water in the presence of an anionic emulsifier, an adhesion promoter (B) which is selected from the reaction product of an aminofunctional amine or a hydrolysate of the latter with an acid anhydride, an epoxyfunctional silane or a hydrolysate of the latter and/or an organosilane having an isocyanate radical and a hydrolysable radical or a hydrolysate of the latter, a colloidal silica (C) and a catalyst (D). The objective of this composition is to make possible linings with a thickness ranging from 40 to 100 .mu.m. Linings of approximately 100 .mu.m are mentioned.
Likewise, European Patent Application EP-A-0,552,983 describes a composition of the same type, obtained from an organopolysiloxane (A) having at least two alkenyl groups, from an organohydropolysiloxane (B) having at least three hydrogen atoms and a crosslinking catalyst (C), by emulsification in water in the presence of an emulsifier. A reinforcing filler, such as a colloidal silica, can be added. The objective, here again, is to make possible linings with a thickness of 40 to 100 .mu.m. A lining of approximately 100 .mu.m is mentioned.